LONDON -- The board of U.K. energy company BP PLC ( BP) has struck a deal to swap its profitable but troublesome Russian oil venture TNK-BP for a big stake in Rosneft, the Kremlin-controlled energy company, a person familiar with the matter said Sunday.

The person said that the sale of BP's half of TNK-BP was expected to net the company between $10 to $15 billion in cash as well as a 15% to 20% stake in Rosneft, Russia's largest producer of oil.

The person said that the ranges were approximate because the parameters of the deal were still being worked out. He spoke on condition of anonymity before an official announcement which he said the companies hoped to make "soon."

Such a deal would allow BP to exit its troubled partnership with the consortium of Russian billionaires that controls the other half of TNK-BP while keeping a presence in Russia, a country responsible for producing nearly 10 million barrels of crude every day.

But the deal would also bring the British company much closer to the Kremlin; Rosneft is run by former deputy prime minister Igor Sechin, a longtime aide to Russian President Vladimir Putin, and BP's shareholders may worry about the political dimensions of the deal.

Britain's The Sunday Telegraph said that five of BP's leading investors, which it didn't identify by name, had qualms about the move.

Rosneft declined to comment when reached by phone late Sunday.

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Nataliya Vasilyeva in Moscow contributed to this report.

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